A controller for controlling a load installed on a vehicle is equipped with a protector that immediately disconnects a circuit when an overcurrent flows to the load. As a conventional example of such a protector, there is known a protector described in JP 2010-239835 A (PTL 1). In PTL 1, the quantities of heat generation and heat radiation of an electricity supply circuit (including a power line connecting a load with a power supply, and a power switch) are calculated on the basis of a current flowing to the load and furthermore, the temperature of the electricity supply circuit is estimated on measurement of the ambient temperature. Then, if an estimated temperature reaches a predetermined threshold value, the controller disconnects the electricity supply circuit to protect a circuit connected to the load.
If the estimated temperature of the electricity supply circuit meets a predetermined temperature condition (for example, a situation where the temperature drops to the ambient temperature), the operation of the controller is switched to a sleep mode (low power consumption mode) and thereby to reduce power consumption. For the reason that current does not flow to the electricity supply circuit connected to the load in a situation where the load is inactivated, the computing load of the controller is reduced by stopping the operation of estimating the temperature of the electricity supply circuit, reducing the power consumption as a whole.